Hybrid low pass diplex filter

Abstract

A hybrid diplex bandstop filter includes a lowpass filter circuit which passes a first range of frequencies and a highpass filter circuit passes a third range of frequencies. The filter blocks a second range of frequencies. The third range of frequencies is higher than the second range and the first range. A tuning circuit tunes at least one re-resonance of a frequency inside the first range of frequencies to either within the second range of frequencies or outside an industry specified upper limit which is in the third range of frequencies.

Description

FIELD OF THE INVENTION[0001]This invention relates generally to the field of diplex filters used in cable television systems, and more particularly to a low pass diplex filter which reduces high pass resonance.BACKGROUND OF THE INVENTION[0002]A diplex circuit, or more simply a “diplexer,” is a device which separates or combines RF signals. Diplexers are used in connection with CATV equipment in a number of situations, some of which use two diplexers back-to-back. These include step attenuators, power bypass circuits, cable simulators and equalizer circuits. Many of the prior art CATV diplex circuits are used to act on signals traveling in so-called forward and return paths, e.g., relatively high frequency RF signals pass from a source of such signals to a television set at subscriber premises in the forward direction over one leg of the circuit while lower frequency (DC) signals pass from the premises in the return direction.[0003]Bandstop or “notch” filters are commonly employed in...

AI Technical Summary

Problems solved by technology

Using typical minimum inductor or capacitor design techniques in the lowpass leg of a diplex bandstop filter creates a problem in achieving a flat upper passband, thus causing return loss and increased delay.

In fact, the values are large enough to create multiple re-resonances in the upper passband of the highpass leg of the filter, which are undesirable.

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